It has been desired that the load carrying capacity of angular contact ball bearings, especially those for use in automobiles, be increased without increasing their sizes. In angular contact ball bearings, balls are held by a resin crown-type cage to be disposed between an inner ring and an outer ring. To increase the load carrying capacity of the bearing, increasing the number of balls which are installed in the cage is effective.
A commonly-used resin crown-type cage for an angular contact ball bearing is formed of a ring portion and a plurality of column portions that protrude from the ring portion in the axial direction and that are arranged in the circumference direction. The column portions next to each other in the circumference direction form pockets that house balls serving as rolling elements. The inner surface of each pocket is formed in a spherical shape so that rotation of the ball is not hindered. To avoid dropping of the ball that is installed in the cage at the time of bearing assembly, each column portion has a column portion radially inward section that forms a bearing-radial-direction inward side portion of the column portion, and a column portion radially outward section (serving as a ball dropping prevention portion for preventing the ball in the pocket from dropping) that is connected to the column portion radially inward section at its radially outer end position, so as to protrude on both sides in the circumferential direction from the column portion radially inward section.
In actual injection molding, a split mold that is opened in the axial direction of the cage is used. In this case, so-called “forcible removal” is performed, that is, the resin is elastically deformed during demolding and the cage is taken out of the mold, in order to form the column portion radially outward section that serves as the ball dropping prevention portion, according to Patent Document 2. The column portion radially outward section has a T-shape so as to protrude on both sides from the thin column portion radially inward section in the thickness direction thereof. Therefore, to perform the forcible removal, a parting line of the split mold need to be set at the position at which the column portion radially outward section is connected to the column portion radially inward section. Patent Documents 1 and 2 each describe a crown-type cage formed by the split mold having the parting line that is set to coincide with the pitch circle position of the row of the balls to be held by the cage.